1. Field of the Invention
The present invention generally relates to semiconductor production methods and metal molds for producing semiconductor devices, and, more particularly, to a method of producing semiconductor devices each having a chip-size package structure and a metal mold for producing such semiconductor devices.
In recent years, there has been an increasing demand for smaller electronic equipment. In response to such a demand, semiconductor devices have been becoming smaller with higher densities. Such semiconductor devices include a chip size package type (hereinafter referred to as xe2x80x9cCSPxe2x80x9d) of a size as close as possible to a semiconductor chip. A semiconductor device of the CSP type is partially provided with resin to improve its reliability while maintaining its smallness. Meanwhile, there is also a demand for semiconductor devices which can be manufactured at high efficiency. To satisfy the two demands, it is necessary to improve productivity and efficiency in the process of providing the resin for a semiconductor device of the CSP type.
2. Description of the Related Art
FIG. 1A shows a CSP-type semiconductor device 1. As shown in this figure, the semiconductor device 1 comprises a semiconductor chip 2, a resin layer 3, and electrodes 4. The resin layer 3 has a predetermined thickness and is formed on a circuit-formation surface having the electrodes 4 of the semiconductor chip 2, so that the circuit-formation surface of the semiconductor chip 2 can be protected by the resin layer 3. The resin layer 3 also, encapsulates the electrodes 4 except the top ends of the electrodes 4 (that are used for electric connection). By encapsulating the electrodes 4, the resin layer 3 also strengthens the attaching of the electrodes 4 to the semiconductor chip 2. The top ends of the electrodes 4 are attached to electrode pads 6 of a printed circuit board 5, thereby mounting the semiconductor device 1 on the printed circuit board 5.
Japanese Laid-Open Patent Application No. 10-71944 discloses a method of forming the resin layer 4 and a metal mold for producing semiconductor devices employed in the method. FIG. 2 shows a metal mold 20 for producing semiconductor devices. The metal mold 20 can be divided into an upper mold 21 and a lower mold 22. The upper mold 21 and the lower mold 22 each have a heater inside (not shown) to heat and melt an encapsulation resin 35 mentioned later. The upper mold 21 moves up and down in directions indicated by arrows Z1 and Z2 in FIG. 2. The lower surface of the upper mold 21 serves as a cavity surface 21a that is almost flat. Accordingly, the upper mold 21 has a very simple shape, and can be produced at a low cost.
Meanwhile, the lower mold 22 is made up of a first sub lower mold 23 and a second sub lower mold 24. The first sub lower mold 23 has a shape corresponding to the shape of a substrate 16, and more specifically, the first sub lower mold 23 has a diameter slightly larger than the diameter of the substrate 16. The substrate 16 is mounted on a cavity surface 25 formed on the upper surface of the first sub lower mold 23. Also, a cavity surface 26 is formed on the side surface of the second sub lower mold 24. In this example, the first sub lower mold 23 is fixed.
The second sub lower mold 24 has an annular shape, surrounding the first sub lower mold 23. The second sub lower mold 24 moves up and down in the directions of the arrows Z1 and Z2 with respect to the first sub lower mold 23.
Immediately after the start of the resin encapsulation process, the second sub lower mold 24 is in a higher state in the direction of the arrow Z2 with respect to the first sub lower mold 23, so that the substrate 16 is mounted in a cavity portion formed by the first and second sub lower molds 23 and 24. Here, the surface of the substrate 17, on which the bumps 12 are provided, faces upward, so that the bumps 12 face the upper mold 21 in the substrate-mounted state.
After the mounting of the substrate 16 in the lower mold 22, a film sheet 30 is attached only to the lower surface of the upper mold 21, and the encapsulation resin 35 is placed on the bumps 12 on the substrate 16. FIG. 3 shows the encapsulation resin 35 placed on a semiconductor chip 11.
The above substrate mounting process is followed by a resin layer forming process. In the resin layer forming process, the metal mold 20 heated to a temperature high enough to melt the encapsulation resin 35, and the upper mold 21 is then moved down in the direction of the arrow Z1.
By moving the upper mold 21 in the direction of the arrow Z1, the upper 21 is first brought into contact with the upper surface of the second sub lower mold 24. Since the lower surface of the upper mold 21 is covered with the film sheet 30 as described above, the film sheet 30 is clamped between the upper mold 21 and the second sub lower mold 24, with the upper mold 21 being in contact with the second sub lower mold 24, as shown in FIG. 4. At this point, a cavity 28 surrounded by the cavity surfaces 21a, 25, and 26 is formed inside the metal mold 20.
Since the encapsulation resin 35 is pressed by the descending upper mold 21 via the film sheet 30 and is heated to a melting temperature, the encapsulation resin 35 can be spread on the substrate 16 to some extent, as shown in FIG. 4.
Once the upper mold 21 is brought into contact with the second sub lower mold 24, the upper mold 21 and the second sub lower mold 24 move further down in the direction of the arrow Z1, with the film sheet 30 being in the clamed state. On the other hand, the first sub lower mold 23 remains in the fixed state. As a result, the cavity 28 becomes smaller as the upper mold 2 and the second sub lower mold 24 move downward, and hence the encapsulation resin 35 is compressed and molded inside the cavity 28. This resin molding technique is called compression mold technique.
FIG. 5 shows a state after the resin layer forming process. In this state, the film sheet 30 is pressed onto the substrate so hard that the top ends of the bumps 12 are lodged in the film sheet 30. Also, the encapsulation resin 35 is spread on the entire surface of the substrate 16, thereby forming a resin layer 13 which encapsulates the bumps 12.
The above resin layer forming process is followed by a separation process. In this process, the upper mold 21 is first moved up in the direction of the arrow Z2. Since the resin layer 13 adheres to the cavity surface 26 of the second sub lower mold 24, only the upper mold 12 is moved upward and separated from the film sheet 30.
The second sub lower mold 24 is then moved down in the direction of Z1 with respect to the first sub lower mold 23. In FIG. 6, the left half defined by a vertical center line shows the state in which the upper mold 21 has been moved up and the second sub lower mold 24 has been moved down. By moving the second sub lower mold 24 downward with respect to the first sub lower mold 23, the resin layer 13 can be separated from the cavity surface 26 of the second sub lower mold 24.
As the resin layer 13 and the cavity surface 26 are separated, the second sub lower-mold 24 starts moving up in the direction of the arrow X2. By doing so, the upper surface of the second low sub mold 24 is brought into contact with the film sheet 30, and the cavity surface 26 is brought into contact with the side face of the resin layer 13. As a result, the substrate 16 is moved upward. Since the film sheet 30 and the resin layer 13 adhere to each other, the substrate 16 is separated from the first sub lower mold 23 when the film sheet 30 is moved upward. The substrate 16 with the resin layer 13 is thus separated from the metal mold 20, as shown in the right half defined by the center line in FIG. 6.
As described so far, the method and device disclosed in the Japanese Laid-Open Patent Application No. 10-71944 greatly reduce the amount of the encapsulation resin 35 for one semiconductor chip 11, thereby reducing the material costs. Also, the resin layer 13 can be more easily formed uniformly on the entire surface of the substrate 16 by the compression mold technique, compared with a conventional transfer mold technique by which resin is injected into a mold.
In the above device, however, only the film sheet 30 is attached to the lower surface of the upper mold 21, and it is impossible to prevent the resin from being brought into contact with the lower mold 22. This results in a poor separability from the metal mold 20 after the resin encapsulation process. Also, the film sheet 30 cannot be kept in tension, and might be wrinkled during the operation of the metal mold 20. The wrinkled film sheet 30 leads to a wrinkled molded product. Furthermore, if a void or impurities exist inside the molded resin layer 13, the reliability of the device will be decreased.
A general object of the present invention is to provide a semiconductor production method and a metal mold for producing semiconductor devices, in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a method of producing semiconductor devices which have an excellent separability from a metal mold after molding so as to almost entirely eliminate the need to clean the metal mold, and a metal mold for producing such semiconductor devices.
Another specific object of the present invention is to provide a method and a metal mold for producing semiconductor devices, by which a resin layer having a desired thickness can be formed from the same amount of encapsulation resin for various types of semiconductor devices, the resin layer surface can be prevented from surface roughening, the encapsulation resin is not spread on the reverse side of a resin layer formed surface, and the resin layer is free from voids and pinholes.
The above objects of the present invention are achieved by a method of producing semiconductor devices, comprising the steps of:
opening a dividable metal mold which comprises a first metal mold having a first cavity forming surface and a second metal mold having a second cavity forming surface, the first metal mold having a first surface facing the second metal mold while the second metal mold having a second surface facing the first metal mold;
disposing a first separation sheet on the first surface including the first cavity forming surface, and a second separation sheet on the second surface including the second cavity forming surface;
attaching the first separation sheet and the second separation sheet closely to the first cavity forming surface and the second cavity forming surface by attracting the first separation sheet and the second separation sheet through a plurality of annular suction portions formed in the dividing surfaces:
placing a substrate provided with a plurality of semiconductor chips on the first separation sheet on the first cavity forming surface;
closing the dividable metal mold so as to form a resin layer by a compression molding technique using an encapsulation resin supplied on the substrate;
opening the dividable metal mold so as to remove the substrate having the resin layer formed thereon from the dividable metal mold opened;
removing the first separation sheet and the second separation sheet from the substrate; and
dividing the substrate into individual semiconductor devices.
In this method, the encapsulation resin is not brought into contact with the first and second metal molds. Accordingly, an excellent separability can be achieved. Even if the encapsulation resin enters between the substrate and the cavity forming surface of the metal mold, the substrate can be surely separated from the dividable metal mold. Also, there is substantially no need to clean the dividable metal mold. Furthermore, in a case where the first metal mold comprises a movable sub metal mold and a fixed sub metal mold, there is no risk of the encapsulation resin entering the gap portion between the movable sub metal mold and the fixed sub metal mold. Thus, wrong operations of the movable sub metal mold and damage on the sliding surface can be prevented. Also, no wrinkles are caused in the separation sheets, so that the resin layer surface of each semiconductor device can be prevented from surface roughening.
The above objects of the present invention are also achieved by a metal mold for producing semiconductor devices by a compression molding technique for resin-encapsulating a substrate provided with a plurality of semiconductor chips. This metal mold comprises: a first metal mold having a first cavity forming surface; a second metal mold having a second cavity forming surface; a plurality of annular suction grooves formed in the dividing surfaces including the first and second cavity forming surfaces; and a vacuum source provided in channels communicating with the suction grooves. The first and second separation sheets are attracted toward the first and second cavity forming surfaces by the vacuum source via the suction grooves.
With this structure, the encapsulation resin does not touch the first and second metal molds. Accordingly, an excellent separability can be achieved. Even if the encapsulation resin enters between the substrate and the cavity forming surface of the metal mold, the substrate can be surely separated from the dividable metal mold. Also, there is substantially no need to clean the dividable metal mold. Furthermore, in a case where the first metal mold comprises a movable sub metal mold and a fixed sub metal mold, there is no risk of the encapsulation resin entering the gap portion between the movable sub metal mold and the fixed sub metal mold. Thus, wrong operations of the movable sub metal mold and damage on the sliding surface can be prevented. Also, no wrinkles are caused in the separation sheets, so that the resin layer surface of each semiconductor device after the molding process can be prevented from surface roughening.